Neuromyelitis optica: a positive appraisal of seronegative cases.

Neuromyelitis optica (NMO) is a rare inflammatory disorder of the central nervous system. The hallmark of NMO is the presence of specific autoantibodies directed against aquaporin 4 (AQP4-IgG). AQP4-IgG, included in diagnostic criteria, has enlarged the clinical spectrum of NMO and serves to predict relapses. Moreover AQP4-IgG has provided unprecedented insight in the immunopathology of NMO, representing a rationale for therapeutic intervention with relevant novel treatment strategies specific for NMO. However, some patients remain seronegative for AQP4-IgG despite a definite diagnosis of NMO and the use of the finest methods for antibody detection. Interestingly, seronegative NMO (NMO(neg)) patients exhibit different demographic and disease-related characteristics in comparison to seropositive patients. The recent association with autoantibodies specific for myelin oligodendrocyte glycoprotein (MOG) is the main indication that disease mechanisms might differ in NMO(pos) and NMO(neg), challenging the position of NMO(neg) patients in the spectrum of demyelinating diseases and therapeutic strategies to be adopted. Thus, a reappraisal of the NMO(neg) population is needed to improve NMO care. Here the current knowledge regarding NMO(neg) is reviewed and hypotheses on its pathogenesis are made including a comprehensive description of detection methods and the prevalence of AQP4-IgG and a review of the epidemiological, clinical and paraclinical characteristics of NMO(neg); finally an integrated view of the general pathophysiological mechanisms underlying NMO(neg) is provided.

Effect of tumor necrosis factor alpha on insulin-dependent diabetes mellitus in NOD mice. I. The early development of autoimmunity and the diabetogenic process.

Tumor necrosis factor (TNF) alpha is a cytokine that has potent immune regulatory functions. To assess the potential role of this cytokine in the early development of autoimmunity, we investigated the effect of TNF on the development of insulin-dependent diabetes mellitus (IDDM) in nonobese diabetic (NOD) mice, a spontaneous murine model for autoimmune, insulin-dependent type I diabetes. Treatment of newborn female NOD mice with TNF every other day for 3 wk, led to an earlier onset of disease (10 versus 15 wk of age in control mice) and 100% incidence before 20 wk of age (compared to 45% at 20 wk of age in control phosphate-buffered saline treated female mice). In contrast, administration of an anti-TNF monoclonal antibody, TN3.19.12, resulted in complete prevention of IDDM. In vitro proliferation assays demonstrated that mice treated with TNF developed an increased T cell response to a panel of beta cell autoantigens, whereas anti-TNF treatment resulted in unresponsiveness to the autoantigens. In addition, autoantibody responses to the panel of beta cell antigens paralleled the T cell responses. The effects mediated by TNF appear to be highly age dependent. Treatment of animals either from birth or from 2 wk of age had a similar effect. However, if treatment was initiated at 4 wk of age, TNF delayed disease onset. These data suggest that TNF has a critical role in the early development of autoimmunity towards beta-islet cells.

Chronic tumor necrosis factor alters T cell responses by attenuating T cell receptor signaling.

Repeated injections of adult mice with recombinant murine TNF prolong the survival of NZB/W F1 mice, and suppress type I insulin-dependent diabetes mellitus (IDDM) in non-obese diabetic (NOD) mice. To determine whether repeated TNF injections suppress T cell function in adult mice, we studied the responses of influenza hemagglutinin-specific T cells derived from T cell receptor (HNT-TCR) transgenic mice. Treatment of adult mice with murine TNF for 3 wk suppressed a broad range of T cell responses, including proliferation and cytokine production. Furthermore, T cell responses of HNT-TCR transgenic mice also expressing the human TNF-globin transgene were markedly reduced compared to HNT-TCR single transgenic littermates, indicating that sustained p55 TNF-R signaling is sufficient to suppress T cell function in vivo. Using a model of chronic TNF exposure in vitro, we demonstrate that (a) chronic TNF effects are dose and time dependent, (b) TNF suppresses the responses of both Th1 and Th2 T helper subsets, (c) the suppressive effects of endogenous TNF produced in T cell cultures could be reversed with neutralizing monoclonal antibodies to TNF, and (d) prolonged TNF exposure attenuates T cell receptor signaling. The finding that anti-TNF treatment in vivo enhances T cell proliferative responses and cytokine production provides evidence for a novel regulatory effect of TNF on T cells in healthy laboratory mice. These effects are more pronounced in chronic inflammatory disease. In addition, our data provide a mechanism through which prolonged TNF exposure suppresses disease in animal models of autoimmunity.

Induction of GAD65-specific regulatory T-cells inhibits ongoing autoimmune diabetes in nonobese diabetic mice.

IDDM is a T-cell-mediated autoimmune disease in which the insulin-producing beta-cells are destroyed. The disease process is complex, involving the recognition of several beta-cell autoantigens. One of these, GAD65, appears to have a critical and not fully defined role in IDDM in humans and in the NOD mouse. We provide evidence that an ongoing diabetogenic response in NOD mice can be suppressed after intravenous administration of GAD65, but not by other beta-cell autoantigens. Furthermore, suppression of the diabetogenic response is mediated by the induction of GAD65-specific CD4+ regulatory T-cells. Finally, cytokine analysis indicates that these CD4+ regulatory T-cells have a T-helper 2 phenotype.

Major histocompatibility complex-encoded antigen processing gene polymorphism in IDDM.

Susceptibility to insulin-dependent diabetes mellitus (IDDM) is greatly influenced by polymorphisms in the genes of the class II region of the human leukocyte antigen (HLA) complex. The complexity of this genetic association and the lack of a direct proof of involvement of HLA class II genes in human IDDM have continued to support speculation on a possible role of genes encoded in the close vicinity of these loci in IDDM. Because the recently discovered transporter associated with antigen processing (TAP) and large multifunctional protease (LMP) genes are encoded in the HLA class II region and are implicated in the processing of antigenic proteins for presentation by HLA class I molecules, they are additional candidates for a role in IDDM pathogenesis. We have analyzed genomic and coding sequence polymorphisms in the LMP2, TAP1, and TAP2 genes of 77 Danish IDDM patients and 102 control subjects. Although patients and control subjects did not differ in TAP1 and LMP2 alleles, we found a striking absence of the TAP2 allele B (long form) in IDDM patients. An analysis of the TAP2 alleles in individual DR types, however, revealed that this phenomenon is likely to be caused by linkage disequilibrium between the two loci. Thus, polymorphisms in the TAP and LMP genes are unlikely to be associated with IDDM.

Role of astrocytes in antigen presentation and naive T-cell activation.

Astrocytes may have a role in antigen presentation in inflammatory diseases of the central nervous system (CNS) such as MS and EAE. In this study, we have assessed whether purified astrocyte cultures could stimulate naive CD4(+) or CD8(+) T-cells from TCR transgenic mice. As previously described, astrocytes sustained antigen-specific CD4(+) T-cell proliferation only in the presence of IFN-gamma, which promotes expression of both MHC class II and B7 molecules on astrocytes. In addition, we show that astrocytes also have the capacity to present antigens to naive CD8(+) T-cell and promote their proliferation. In one system, this CD8(+) T-cell proliferation was dependent on IFN-gamma-induced upregulation of B7 molecules on astrocytes. However, in a second TCR transgenic system, astrocytes could induce naive CD8(+) T-cell proliferation even in the absence of IFN-gamma. The possible implications of these findings for the pathophysiology of CNS inflammatory diseases are discussed.

The prevalence of selective IgA deficiency in type 1 diabetes mellitus.

A significant increase in the prevalence of selective IgA deficiency has been observed in patients with autoimmune disorders such as systemic lupus erythematosus and rheumatoid arthritis. Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease and susceptibility to both IDDM and IgA deficiency is associated with HLA DQB1 alleles encoding non-Asp amino acids at position 57. In order to assess whether the prevalence of selective IgA deficiency is increased in IDDM, we have screened a homogeneous series of adult patients with IDDM for selective IgA deficiency. One patient (1:261) was found to have a selective IgA deficiency. The prevalence of selective IgA deficiency among adult French blood donors is 1:1400. Thus, although IDDM and selective IgA deficiency are both associated with the presence of non-Asp amino acids at position 57 of the HLA DQ beta chain, the frequency of this immunodeficiency in adult IDDM patients is not significantly increased.

Role of CD8 T cell subsets in the pathogenesis of multiple sclerosis.

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system leading to demyelination and axonal/neuronal loss. Cumulating evidence points to a key role for CD8 T cells in this disabling disease. Oligoclonal CD8 T cells reside in demyelinating plaques where they are likely to contribute to tissue destruction. Histopathological analyses and compelling observations from animal models indicate that cytotoxic CD8 T cells target neural cell populations with the potential of causing lesions reminiscent of MS. However, CD8 T cell differentiation results in several subsets of effector CD8 T cells that could be differentially implicated in the mechanisms contributing to tissue damage. Moreover CD8 regulatory T cells arise as important populations involved in restoring immune homoeostasis and in maintaining immune privileged sites. Here we examine the current literature pertaining to the role of CD8 effector and regulatory T cell subsets in the pathogenesis of MS.

Hepatitis B vaccination and central nervous system demyelination: an immunological approach.

Demyelination events or multiple sclerosis following hepatitis B virus (HBV) vaccination have been reported. We therefore compared the T-cell response to HBsAg in patients with CNS demyelination following HBV vaccination and in HBV-vaccinated healthy individuals. Our data showed no differences in terms of T-cell proliferation or cytokine production between these groups and may help to allay concerns that HBV vaccination might trigger a deleterious immune response.

CD4+ T cell mediated intestinal immunity: chronic inflammation versus immune regulation.

BACKGROUND: Several studies have suggested that chronic inflammatory bowel disease may be a consequence of antigen specific recognition by appropriate T cells which expand and induce immunopathology. AIMS: We wished to investigate whether autoreactive CD4+ T cells can initiate the disease on recognition of enterocyte specific antigens directly and if induction of mucosal tolerance occurs. METHODS: Transgenic mice (VILLIN-HA) were generated that showed specific expression of haemagglutinin from influenza virus A exclusively in enterocytes of the intestinal epithelium. To investigate the impact of enterocyte specific haemagglutinin expression in an autoimmune environment, we mated VILLIN-HA mice with T cell receptor (TCR)-HA mice expressing an alpha/beta-TCR, which recognises an MHC class II restricted epitope of haemagglutinin, and analysed the HA specific T cells for induction of autoimmunity or tolerance. RESULTS: In VILLIN-HAxTCR-HA mice, incomplete central deletion of HA specific lymphocytes occurred. Peripheral HA specific lymphocytes showed an activated phenotype and increased infiltration into the intestinal mucosa, but not into other organs of double transgenic mice. Enterocyte specific lamina propria lymphocytes showed a dose dependent proliferative response on antigen stimulation whereas the proliferative capacity of intraepithelial lymphocytes was reduced. Mucosal lymphocytes from VILLIN-HAxTCR-HA mice secreted lower amounts of interferon gamma and interleukin (IL)-2 but higher levels of tumour necrosis factor alpha, monocyte chemoattractant protein 1, and IL-6. Mucosal immune reactions were accompanied by broad changes in the gene expression profile with expression of proinflammatory genes, but strikingly also a remarkable set of genes discussed in the context of peripheral induction of regulatory T cells, including IL-10, Nrp-1, and Foxp3. CONCLUSIONS: Enterocyte specific antigen expression is sufficient to trigger a specific CD4+ T cell response leading to mucosal infiltration. In our model, progression to overt clinical disease was counteracted most likely by induction of regulatory T cells.

Recent advances in immunology in multiple sclerosis.

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system that is of possible autoimmune origin. This article is divided into three parts, reviewing recent advances in three selected topics regarding the immunology of multiple sclerosis. The first part addresses the consequences of T cell and oligodendrocyte death in the inflammatory lesions. The second covers the recent experimental evidence favouring the involvement of infectious agents in the pathophysiology of central nervous system autoimmune diseases. The third part concerns the mode of action of interferon-beta in multiple sclerosis. These new advances have lead to a better understanding of the immunopathology of multiple sclerosis and therefore open new therapeutic possibilities.

Selective IgA deficiency and autoimmunity.

Selective IgA deficiency is the most common primary immunodeficiency. Selective IgA deficiency, as most other immunodeficiencies, is frequently associated with autoimmune phenomena. In this article the authors critically review the literature concerning this association, and discuss the possible mechanisms leading to the increased frequency of autoimmune disorders in subjects with selective IgA deficiency.

Th1 and Th2 CD4+ T cells in the pathogenesis of organ-specific autoimmune diseases.

CD4+ T cells play a key role in regulating immune system function. When these regulatory processes go awry, organ-specific autoimmune diseases may develop. Here, Roland Liblau, Steven Singer and Hugh McDevitt explore the thesis that a particular subset of CD4+ T cells, namely T helper 1 (Th1) cells, contributes to the pathogenesis of organ-specific autoimmune diseases, while another subset, Th2 cells, prevents them.

The roles of Fas/APO-1 (CD95) and TNF in antigen-induced programmed cell death in T cell receptor transgenic mice.

The possible involvement of Fas/APO-1 (CD95) and TNF in antigen-specific AICD of thymocytes and mature T cells has been investigated. Antigenic stimulation in vivo of influenza hemagglutinin (HA)-specific TCRtg mice was used to demonstrate that the kinetics of thymocyte and peripheral CD4+ T cell deletion are similar in mice with normal (+/+) or defective Fas (lpr/lpr) background, indicating that a Fas-independent pathway(s) is responsible for the deletion of activated T cells. TCRtg-+/+ or TCRtg-lpr/lpr mice injected with murine TNF-blocking MAb (TN3) showed rapid apoptosis of thymocytes after HA stimulation, indicating that death signaling through Fas and TNF receptors is not essential for HA-induced thymocyte deletion. CDC peripheral T cells in TCRtg-lpr/lpr mice did not undergo apoptosis following injection with HA and TN3, indicating that TNF-mediated apoptosis is involved in the deletion of mature T cells after antigenic stimulation. However, apoptosis still occurred in TCRtg-+/+ mice injected with TN3, indicating that both Fas- and TNF-mediated cell death can contribute to the deletion of activated peripheral T cells.

Administering glutamic acid decarboxylase to NOD mice prevents diabetes.

Type 1 diabetes is the result of an ongoing autoimmune response to specific proteins expressed by the insulin producing beta cells. Recently, a number of beta cell autoantigens have been identified. However, their role in mediating the diabetogenic response is not known. Here we assess the relative importance of a panel of beta cell autoantigens in the disease process. The approach was to inhibit T cell proliferation to a given autoantigen by either i.t. or i.v. injections, and then determine the effect this had on the diabetogenic response. We show that administering murine glutamic acid decarboxylase (GAD) to 3-week-old NOD females can reduce the frequency of insulitis and prevent the onset of diabetes. In contrast, carboxypeptidase H or peripherin do not induce a similar protective effect, suggesting that GAD has a critical role in the diabetogenic response. These results also suggest that GAD may provide a useful target for antigen-specific immunotherapy.

Role of autoreactive CD8+ T cells in organ-specific autoimmune diseases: insight from transgenic mouse models.

There is now convincing evidence that autoreactive CD8+ T cells can contribute to the pathogenesis of organ-specific autoimmune diseases. In the non-obese diabetic mouse, there is direct evidence that beta-islet cell-specific CD8+ cytotoxic T cells have a pathogenic effect. In human diseases such as autoimmune diabetes and multiple sclerosis, indirect evidence also suggests a role for CD8+ T cells in tissue damage, although their antigen specificity is unknown. Transgenic mouse models as well as the use of knockout mice have been instrumental in the identification of the role of autoreactive CD8+ T cells. Spontaneous models of CD8+ T-cell-mediated autoimmunity generated through transgenesis should help delineate the effector mechanisms leading to tissue destruction. The study of autoreactive CD8+ T cells and the characterization of their antigenic specificity should help unravel the pathophysiology of organ-specific autoimmune diseases, help identify exacerbating foreign antigens, and allow the design of antigen-specific immunotherapy targeting the pathogenic autoreactive T cells.

Chronic intravenous injections of antigen induce and maintain tolerance in T cell receptor-transgenic mice.

Antigen-specific T cell tolerance can be induced by systemic injection of high-dose antigen. In particular, a single intravenous (i.v.) injection of influenza virus hemagglutinin peptide in HNT-TCR transgenic mice induces T cell tolerance through thymocyte apoptosis as well as anergy and deletion of peripheral CD4+ T cells. We now show that this tolerance is reversed after 8 weeks probably due to the short in vivo half-life of the peptide. Since durable tolerance is required for this strategy to be of therapeutic value, we tested whether weekly i.v. injections of peptide (up to 12 weeks) could maintain the CD4+ T cell tolerance. Each injection induces a profound deletion of thymocytes, although their level recovers before the next injection. Therefore, during the treatment period, the thymus undergoes cycles of contraction/expansion. In the periphery, the number of CD4+ T cells is stably decreased and the persisting CD4+ T cells are hyporeactive both in vitro and in vivo. This tolerance is essentially peripheral since comparable results were obtained in thymectomized HNT-TCR mice injected weekly. Our data show that stable antigen-specific tolerance can be induced by repeated i.v. injections of antigen. These findings might have implications for the treatment of T cell-mediated autoimmune diseases.

Immune response to glutamic acid decarboxylase correlates with insulitis in non-obese diabetic mice.

Knowing the autoantigen target(s) in an organ-specific autoimmune disease is essential to understanding its pathogenesis. Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease characterized by lymphocytic infiltration of the islets of Langerhans (insulitis) and destruction of insulin-secreting pancreatic beta-cells. Several beta-cell proteins have been identified as autoantigens, but their importance in the diabetogenic process is not known. The non-obese diabetic (NOD) mouse is a murine model for spontaneous IDDM. Here we determine the temporal sequence of T-cell and antibody responses in NOD mice to a panel of five murine beta-cell antigens and find that antibody and T-cell responses specific for the two isoforms of glutamic acid decarboxylase (GAD) are first detected in 4-week-old NOD mice. This GAD-specific reactivity coincides with the earliest detectable response to an islet extract, and with the onset of insulitis. Furthermore, NOD mice receiving intrathymic injections of GAD65 exhibit markedly reduced T-cell proliferative responses to GAD and to the rest of the panel, in addition to remaining free of diabetes. These results indicate that the spontaneous response to beta-cell antigens arises very early in life and that the anti-GAD immune response has a critical role in the disease process during this period.

A small number of residues in the class II molecule I-Au confer the ability to bind the myelin basic protein peptide Ac1-11.

The N-terminal peptide Ac1-11 of myelin basic protein induces experimental autoimmune encephalomyelitis in H-2(u) and (H-2(u) x H-2(s)) mice but does not in H-2(s) mice. Ac1-11 binds weakly to the class II major histocompatibility complex (MHC) molecule I-Au but not at all to I-As. We have studied the interaction of Ac1-11 and I-Au as a model system for therapeutic intervention in the autoimmune response seen in experimental autoimmune encephalomyelitis. Two polymorphic residues that differ between I-Au and I-As, Y26beta and T28beta, and one conserved residue, E74beta, confer specific binding of Ac1-11 to I-Au. A fourth residue, R70beta in I-Au, affects both peptide binding and T cell recognition. These results are consistent with a model that places arginine at position five of Ac1-11 in pockets 4 and 7 of the MHC groove, which is formed in part by residues 26, 28, 70, and 74 of Abetau and places lysine at position four of Ac1-11, previously shown to be a major MHC contact, in hydrophobic pocket 6. The data indicate that the primary region of I-Au that confers specific binding of Ac1-11 lies in the center of the peptide binding groove rather than in the region that contacts the N terminus of the peptide, as has been shown for HLA DR and the homologous I-E molecules.

Intravenous injection of soluble antigen induces thymic and peripheral T-cells apoptosis.

The mechanism by which tolerance is induced via systemic administration of high doses of aqueous antigen has been analyzed by using mice transgenic for a T-cell receptor specific for the influenza virus hemagglutinin (HA) peptide comprising amino acids 126-138. After intravenous injection of 750 (but not 75) micrograms of HA peptide, a state of hyporesponsiveness was rapidly induced. In the thymus, in situ apoptosis in the cortex and at the corticomedullary junction was responsible for a synchronous and massive deletion of CD4+ CD8+ thymocytes. In secondary lymphoid organs, HA-reactive T cells were initially activated but were hyporesponsive at the single cell level. After 3 days, however, those cells were rapidly deleted, at least partially, through an apoptotic process. Therefore, both thymic and peripheral apoptosis, in addition to T-cell receptor desensitization, contribute to high-dose tolerance.